1. Field of the Invention
This invention relates to a lubricant and surface conditioner for metal surfaces, more particularly metal surfaces already in the size and shape of their intended consumer use (such surfaces sometimes being briefly denoted hereinafter as "formed"), still more particularly to such a lubricant and surface conditioner which improves the mobility of aluminum cans without adversely affecting the adhesion of paints or lacquers applied thereto; maintains this mobility enhancing effect even if subjected to more than normal heating, for example if a can production and cleaning line stalls temporarily in such a fashion as to leave some cans in the drying oven for several times longer than in normal production; and is reasonably stable in storage under normal warm to hot conditions, even when all the active ingredients are stored together.
2. Discussion of Related Art
Aluminum cans are commonly used as containers for a wide variety of products, especially beverages. In the most widely used current commercial practice, at least for large scale operations, the aluminum cans are typically washed with acidic cleaners to remove aluminum fines and other contaminants therefrom. More particularly, aluminum cans are subjected to a succession of six cleaning and rinsing operations as described in Table 1 below.
TABLE 1 ______________________________________ STAGE ACTION ON SURFACE NUMBER DURING STAGE ______________________________________ 1 Aqueous Acid Precleaning 2 Aqueous Acid and Surfactant Cleaning 3 Tap Water Rinse 4 Mild Acid Postcleaning, Conversion Coating, or Tap Water Rinse 5 Tap Water Rinse 6 Deionized ("DI") Water Rinse ______________________________________
The cleaning of aluminum cans generally results in differential rates of metal surface etch on the outside versus on the inside of the cans. For example, optimum conditions required to attain an aluminum fine-free surface on the inside of the cans usually leads to can mobility problems on conveyors because of the increased roughness on the outside can surface, unless some material to avoid this problem is put into place on the outside surface of the cleaned cans.
These aluminum can mobility problems are particularly apparent when it is attempted to convey the cans through single filers and to printers. Thus, a need has arisen in the aluminum can manufacturing industry to modify the coefficient of static friction (hereinafter often abbreviated as "COF") on at least the outside surface of the cans to improve their mobility. The reason for improving the mobility of aluminum cans is the general trend in this manufacturing industry to increase production without additional capital investments in building new plants. The increased production demand is requiring can manufitcturers to increase their line and printer speeds to produce 20 to 40 percent more cans per unit of time. For example, the maximum speed at which aluminum cans, in the absence of any treatment to reduce their coefficient of surface friction, may be passed through a printing station typically is on the average of about 1150 cans per minute, whereas it is desired that such rate be increased to about 1400 to 1500 cans per minute or even higher.
However, aluminum cans thoroughly cleaned by either acid or alkaline cleaner are, in general, characterized by high surface roughness and thus tend to have a high coefficient of static friction. This property hinders the flow of cans through single filers and printers when attempting to increase their line speed. As a result, printer misfeeding problems, frequent jammings, down time, and loss of production can occur in addition to high rates of can spoilage.
Another consideration in modifying the surface properties of aluminum cans is the concern that such modification may interfere with or adversely affect the ability of the can to be printed when passed to a printing or labeling station. For example, after cleaning the cans, labels may be printed on their outside surface, and lacquers may be sprayed on their inside and/or outside surface. In such a case, the adhesion of the paints and lacquers is of major concern.
It is currently possible to produce a can which is satisfactorily mobile and to which subsequently applied inks and/or lacquers have adequate adhesion by using suitable surfactants either in Stage 4 or Stage 6 as noted above. Preferred treatments for use in Stage 6 are described in U.S. Pat. Nos. 4,944,889 and 4,859,351 and in U.S. application Ser. No. 07/910,483, and some of them are commercially available from the Parker+Amchem Division of Henkel Corporation (hereinafter often abbreviated as "P+A") under the name ME-40.RTM.. However, many manufacturers have been found to be reluctant to use chemicals such as ME-40.RTM. in Stage 6. In some cases, this reluctance is due to the presence of a carbon filter for the DI water (normal Stage 6) system, a filter that can become inoperative by adsorption of chemicals such as those in ME-40.RTM.; in other cases, it is due to a reluctance to make the engineering changes necessary to run ME-40.
The above noted U.S. patent application, along with U.S. Pat. Nos. 5,030,323 and 5,064,500, also describes preferred treatments for use in Stage 4, and some of these materials are commercially available from P+A under the name FIXODINE.RTM. 500. However, the reduction in coefficient of friction provided by the latter treatment can be substantially reduced, often to an unacceptable level, if the treated cans are subjected to extraordinary heating after completion of the six process stages described above. Such extraordinary heating of the cans in the drying oven occurs whenever a high speed production line is stalled for even a few minutes, an event that is by no means rare in practice. In practical terms, the higher COF measurements correlate with the loss of mobility, thereby defeating the purpose of introducing mobility enhancing surfactants into Stage 4 can washing formulations.
It has also been observed that the coefficient of friction on can surfaces is less effectively reduced by FIXODINE.RTM. 500 if the commercially supplied concentrate(s), especially if supplied as a single concentrate containing all the required ingredients except water, but even if supplied in two separate packages with most of the acid content in a separate package from the phosphate ester component needed, is stored for several weeks at temperatures at or above 45.degree. C., which can easily be reached in storage areas in summer in most of the United States.
A major object of the invention is to provide adequate mobility enhancement without practically significant deterioration of subsequent adhesion to the treated surface by printing ink or lacquer, as little deterioration as possible of this mobility enhancement under extended heating at temperatures typical for drying ovens on high speed can lines, and stability to storage in hot weather of a concentrate or pair of concentrates suitable for diluting with water to make the working solution for direct treatment of cans, suitable for use in Stage 4 as defined above, and without requiring the use of any additive to the DI water used in Stage 6.